PUBLIC SUPEBVISTOX 197 



" milk " was found to consist of a mixture of water, 

 white pigment, common salt and a little skimmed milk. 



There is no general rule as to the frequency of adul- 

 teration. In some cities, it does not appear to be partic- 

 ularly frequent, while in others it is very common. 



Besides the adulterations found upon official exam- 

 inations of the market milk in cities, the question of 

 fraud sometimes arises in connection with the milk deliv- 

 ered to creameries. In the creameries, it is customary 

 to use some quick method for determining the approx- 

 imate fat content of the milk that is delivered by the 

 various patrons. 



In the official control of milk in cities two pruvieional 

 or preliminary tests have long been uscil and these are 

 still depended on to some extent; they consist in the de- 

 termination of the specific gravity and in a test of the 

 transparency. Even when used in conjunction, these 

 tests are not to be relied upon very far, but they can be 

 used, if with sufficient caution, to determine whether a 

 more thorough examination be necessary. If it is de- 

 cided that a laboratory examination is re([uired, a sam- 

 pk' should be taken with great care, and sealed and 

 delivered to the ai)i)ropriate expert for analysis. 



The specific gravity of cow's milk varies between 

 about 1.0:27 and 1.040 at 15 ^ C. (60^ F.) ; but such differ- 

 ences are to be found only in the milk of certain indi- 

 vidual cows. The siiecific gravity of mixed-herd milk 

 usually falls between 1.028 and 1.034. If the specific 

 gravity is either above or below these limits it is always 

 sus])icious. [The average specific gravity is l.O.'i^.J 



Many different forms of apparatus have been pro- 

 posed for measuring tlic fransparency of milk, to deter- 

 mine if it is or is not diluted. However, these instru- 

 ments are all defective and the results obtained by their 

 use are not to be regarded as of any value except to indi- 



